The brokerage said Groupon Goods, the company's consumer products category, is increasingly becoming the merchant of record - the owner of goods being sold or the first-party seller.

As first-party sales assume inventory risk and drive higher revenue contribution, the composition of Groupon's first-quarter revenue beat in North America has become questionable, analyst Ken Sena wrote in a note.

"Growth in unique visitors in the U.S. to Groupon.com, which can be looked at as a proxy for subscriber growth, exhibited negative year-over-year trends this quarter," Sena said.

Essentially, no one is buying stuff from Groupon, which leaves them holding the bag on lots of it.